Unnecessary elaboration about not being assignable to type parameters (#42952)

tests/cases/compiler/doNotElaborateAssignabilityToTypeParameters.ts

@@ -0,0 +1,13 @@
+// @lib: es2015
+// @target: ES5
+async function foo<T>(x: T): Promise<T> {
+  let yaddable = await getXOrYadda(x);
+  return yaddable;
+}
+
+interface Yadda {
+  stuff: string,
+  things: string,
+}
+
+declare function getXOrYadda<T>(x: T): T | Yadda;